In Japanese Patent Application Laid-Open No. 2000-97742, there is disclosed a Doppler ultrasonic flowmeter that permits precise, highly accurate and contactless measurement on a time-dependant basis even in the case of a flow in an unsteady state.
Patent document 1: Japanese Patent Application Laid-Open No. 2000-97742.
The Doppler ultrasonic flowmeter disclosed here has a structure as described below. Specifically, it has an ultrasonic transmitting means emitting an ultrasonic pulse of a predetermined frequency from an ultrasonic transducer into the fluid to be measured along a measurement line, a fluid velocity distribution measuring means receiving, out of the ultrasonic pulses emitted into the fluid to be measured, an ultrasonic echo reflected from a measurement region to thereby measure a flow velocity distribution of the fluid to be measured in the measurement region and a flow rate computing means performing an integration on the basis of the flow velocity distribution of the fluid to be measured. The flow rate computing means measures the flow rate based on the flow velocity distribution of the fluid to be measured in the measurement region.
This Doppler ultrasonic flowmeter measures the flow velocity distribution of the fluid to be measured which flows in a pipe, and exhibits an excellent performance in response to the flow rate in a transiting duration in which temporal fluctuations are seen. Further, even at a part in which the flow of the fluid is insufficient or at a place in which the flow is three-dimensional, for example, at a place of the pipe just after it is bent such as of an elbow pipe or a U-shaped inversion pipe, it is possible to measure the flow rate of the fluid to be measured efficiently, highly accurately and instantly. In comparison with conventional ultrasonic flowmeters offered therebefore, as a feature, the Doppler ultrasonic flowmeter can perform the measurement experimental values, empirical values and so forth, being highly evaluated.
Meanwhile, when the above-described Doppler ultrasonic flowmeter measures the flow velocity distribution (flow rate) by taking advantage of a Doppler effect of ultrasonic pulses, reflective bodies are required in the fluid to cause Doppler shifts. When the fluid has no reflective body therein, the measurement is impossible. Still, when the refractive bodies are not mixed into the fluid uniformly, the flow velocity distribution lacks, so that the accurate flow velocity distribution can not be obtained.
When the fluid to be measured is the fluid (for example, water), as a refractive body, a gas having largely different acoustic impedance therefrom such as air or helium is preferable. However, the injection of the gas was performed using a nozzle inserted into the fluid pipe, a sufficient refractive echo intensity could not be obtained unless the gas grows to a size appropriate for the reflection of the ultrasonic waves used for the measurement in the fluid to be measured. Besides, it is impossible to obtain the appropriate flow velocity distribution unless the gas is dispersed uniformly in the emitting direction of the ultrasonic pulses.
An object of the present invention is to provide a measurement technology enabling to measure the flow rate more accurately even under an environment where the contained refractive bodies are not sufficient, by way of uniformly injecting such bubbles into the fluid to be measured that have the size suitable for the predetermined frequency of the ultrasonic pulses.
Therefore, in one embodiment, a bubble generator is used to bring out the performance of a Doppler ultrasonic flowmeter to the maximum extent.
Further, in another embodiment a Doppler ultrasonic flowmeter is provided with a bubble generator to bring out the performance to the maximum extent.